Carbon nanotubes have been used by many for field emission applications. Carbon nanotubes (CNTs) come in two families, single wall nanotubes (SWNTs) and multi-wall nanotubes (MWNTs). Both materials are long (11–10,000 microns) and thin (0.001–0.1 microns in diameter). This high aspect ratio and the fact that they are semiconducting or metallic makes them ideal candidates for field emission applications. One problem, however, is if the CNTs are too densely packed, the CNTs shield each other from the strong electrical fields needed to extract the electrons from the material. The field emission from these materials is further improved if the CNT fibers are aligned in parallel to the applied electrical field. Also desired is an inexpensive way of applying the CNT material onto suitable substrate materials at low temperature and aligning these materials using methods that are suitable for large-scale manufacturing.
By growing CNTs directly on a catalyst, some success has been achieved in growing the CNT materials with acceptable density and alignment, but not always in a predictable fashion. Furthermore, the growth temperatures are high, too high for using low-temperature sodalime glass that is commonly used in the display industry.